1. Field of Invention
This invention relates to certain ethane diimidic acid bis[(arylalkylidene)hydrazide compounds, and particularly to certain ethanediimidic acid bis[(o-hydroxyarylalkylidene)hydrazide] color-formers, to their reactions with metal salts to form colored coordination compounds, and to imaging systems based thereon. The formation of colored coordination compounds can be employed to generate images and is important in the manufacture and use of pressure-sensitive transfer papers for preparing carbonless copies.
The invention also concerns the admixture of these certain color-formers with N-(monosubstituted)dithiooxamides and/or N,N'-(disubstituted)dithiooxamides to form images of various colors and preferably black images during the application of appropriate pressure to pressure sensitive imaging constructions such as carbonless paper constructions.
2. Background of the Art
The use of coordination compounds to form imaging sheets has been important in the field of pressure sensitive transfer papers useful for preparing carbonless copies. The present invention provides color-forming compositions which, when complexed with transition metal ions, can provide compositions that exhibit light absorption characteristics such that they appear as intensely yellow colored complexes. This is accomplished in the present invention by the use of certain colorless ethanediimidic acid bis[(arylalkylidene)hydrazide] compounds, and particularly to certain bis[(o-hydroxy arylalkylidene)hydrazide] compounds which provide an intense yellow color when individually complexed with cations of certain transition metals as, for example, nickel.sup.2+.
The ethanediimidic acid bis[(arylalkylidene)hydrazide] color-forming compounds which are useful in the present invention and are capable of forming colored complexes with transition metal salts can be represented by the following formula, I, as follows; ##STR1## wherein R.sub.1 is selected from the group of substituents comprising an aryl group; particularly phenyl, substituted phenyl, naphthyl, and substituted naphthyl; and most particularly is selected from the group of aromatic substituents consisting of phenyl, substituted phenyl, naphthyl and substituted naphthyl containing an hydroxy group adjacent (i.e., ortho) or pseudo adjacent (i.e., peri) to the site of attachment of the carbon atom attached by a double bond to the nitrogen atom; and R.sub.2, R.sub.3, and R.sub.4, are substituents independently selected from the group of substituents consisting of hydrogen, alkyl group, aryl, substituted aryl, and R.sub.1.
The invention also includes within its scope, new ethanediimidic acid bis[(o-hydroxyarylalkylidene)hydrazide] compounds and derivatives of these compounds whereby alkyl groups are substituted on the o-hydroxysubstituted aromatic rings. These new compounds are very soluble in the solvents favored in the encapsulation processes employed in carbonless imaging constructions and the preferred compounds are also low in volatility. When these bishydrazides react with certain metal salts, and especially with nickel salts, strongly yellow-colored coordination complexes are formed. The invention also includes within its scope new coordination complexes of ethanediimidic acid bis[(o-hydroxyarylalkylidene)hydrazide] compounds with various transition metals such as Ni.sup.2+.
The ligands of the present invention are derivatives of the parent compound, variously known as, oxalimidic acid dihydrazide, oxamide dihydrazone, imidic dihydrazide, oxalimidrazone, and ethanediimidic acid dihydrazide. Chemical Abstracts 11th Collective Index prefers the name ethanediimidic acid dihydrazide. The Chemical Abstracts Registry Number for this compound is [3457-37-2]. The reaction of ethanediimidic acid dihydrazide with aldehydes and ketones forms compounds named as ethanediimidic acid bis[hydrazides]. For example, condensation of 2 molecules of benzaldehyde with one molecule of ethanediimidic acid dihydrazide affords ethanediimidic acid bis[(phenylmethylene)hydrazide]. The Chemical Abstracts Registry number for this compound is [6642-48-4]. This compound can also be named as ethanediimidic acid bis[(benzylidene)hydrazide]. Herein we refer to compounds derived from the condensation of aromatic aldehydes and ketones with ethanediimidic acid dihydrazide as ethanediimidic acid bis[(arylalkylidene)hydrazide] compounds. Similarly, compounds derived from the condensation between aliphatic aldehydes and ketones with ethanediimidic acid dihydrazide are referred to as ethanediimidic acid bis[(alkylidene)hydrazides].
Condensation of the parent compound with compounds containing two ketone or two aldehyde groups to form polymers has been reported (see P. M. Hergenrother, Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem. 974, 781) as has their use in the formation of polymers containing heterocyclic compounds (see P. M. Hergenrother; M Hudlicky, J. Fluorine Chem. 1978, 12, 439). Condensation with dicarboxylic acid chlorides to form polymers has also been reported (see M. Saga; T. Shono, J. Polym. Sci., Part B 1966, 4, 869).
In contrast to its use in the preparation of polymers, the reaction of ethanediimidic acid dihydrazide with simple aldehydes and ketones has been less studied. The reactions of the this dihydrazide with various aldehydes and ketones was investigated by Dedichen (see G. Dedichen, Avhandl. Norske Videnskaps-Akad. Oslo, I, Mat.-Naturv. Klasse 936, No. 5; Chem. Abstr. 1937. 31, 4985.sup.3). Although the author investigated the coordination chemistry of ethanediimidic acid dihydrazide with metals such as copper, mercury, lead, bismuth, and nickel, no discussion of the coordination of aldehyde and ketone condensation products with metals is given. More recently, Pyl and coworkers prepared a series of ethanediimidic acid bis[(.alpha.-(chloromethyl)aryl)methylene] hydrazide compounds (see T. Pyl; L. Seidl; H. Beyer Chem. Ber. 1968, 101, 29). They also did not report on the coordination of these compounds with metals. Biswell found that ethanediimidic acid bis[(o-hydroxyarylalkylidene)hydrazide] ligands were useful as stabilizers for fats, drying oils, rubbers, and other synthetic unsaturated substances subject to deterioration by the action of oxygen in the presence of transition metal ions such as Cu.sup.2+ and Co.sup.2+ . These ligands served to decrease the metal's ability to catalyze oxidation by forming complexes with the metal ion. A structure for the metal complex was proposed. See C. B. Biswell, U.S. Pat. No. 2,551,786 (1951).
In none of the above cited literature have the ligands or coordination compounds been used in any imaging process, nor has any reference to imaging been made, nor has any mention of the requirements of encapsulation been disclosed, nor has any mention been made of the colors the these complexes.
In order to be useful in one embodiment of an imaging construction, it is desirable that the ligand be capable of being encapsulated and of rapidly forming a stable colored image upon contact with a metal cation on a receptor sheet. That is, the transition metal complex should form nearly instantaneously, so that the image is rapidly formed as the stylus pressure is applied to the backside of the donor sheet. This will help ensure formation of an accurate, almost instantly readable copy. The image should also be relatively stable so that it does not substantially fade with time.
One type of carbonless imaging chemistry takes advantage of the fact that dithiooxamide compounds are encapsulable and react readily with many transition metal salts to form coordination complexes. The chemistry and characteristics of certain dithiooxamide materials have been used successfully in commercially available carbonless paper products. Generally, these dithiooxamide compounds comprise symmetrically disubstituted dithiooxamide compounds and include N,N'-dibenzyldithiooxamide and N,N'-di(2-octanoyloxyethyl)dithiooxamide.
Transition metal salts used to form coordination complexes with dithiooxamides which have been employed in the preparation of carbonless image transfer products or constructions are generally those comprising cations having a +2 valance state. Compounds with nickel, zinc, palladium, platinum, copper and cobalt all form such complexes with dithiooxamides. Many of these coordination complexes are deeply colored.
Carbonless imaging constructions, or products employing this chemistry, generally involve placement of one reactant (i.e., one of the transition metal or ligand) on one substrate (for example, sheet of paper) and the other reactant (the one of transition metal or ligand not used on the first substrate) on a second, i.e., mating, substrate. The ligand and metal are maintained separated from contact and reaction with one another. This is typically accomplished by encapsulation of one of the reactants. Herein, the terms "encapsulation" and "encapsulated compounds" refer to microcapsules enclosing a fill material therewithin.
Once rupturing pressure is applied to the construction, as from a stylus or business-machine key, the solution of encapsulated reactant is released, and a complex between the previously separated reactants is formed. In general, the resulting complex will, of course, form a colored image corresponding to the path traveled by the stylus, or the pattern of pressure provided by the key.
In one commercial product, the capsules on a first sheet (donor sheet) contain dithiooxamide (DTO) derivatives, and the mating sheet, sometimes referred to as the receptor sheet, contains a coating of selected salts of nickel. The encapsulated dithiooxamide ligands, in a suitable binder, are coated onto one face of the donor sheet; and, the metal salt, optionally in a suitable binder, is coated onto one face of the receptor sheet. Herein, the term "suitable binder" refers to a material, such as starch, polymer, or latex, that allows for dispersion of the reactants in a coating on a substrate, promotes adhesion of the capsules to the substrate, and permits the capsules to be ruptured under hand-held stylus pressure, or typical business machine key pressure. When the two coated faces are contacted such that the ligands and the metal salt can combine and react, a coordination complex forms and an image results. Typically, this occurs by transfer of the ligand to the site of the metal salt, i.e., transfer of the ligand from the donor sheet to the receptor sheet. The image, of course, forms on the receptor sheet.
In a preferred orientation, the encapsulated ligands, in a suitable binder, are coated on the back of the donor sheet, sometimes referred to as a coated back (CB) sheet, and the metal salt, optionally in a suitable binder, is coated on the front of the receptor sheet, or coated front (CF) sheet. Again, in imaging, the two sheets are positioned such that the encapsulated ligands on the donor (CB) sheet faces the metal salt coating on the receptor (CF) sheet. When pressure is applied to the uncoated surface of the donor sheet, (i.e., the face not in contact with the receptor (CF) sheet), selected capsules rupture (i.e., those capsules corresponding to the pattern of applied pressure) with release of the ligand for transfer to the receptor sheet, forming a colored pattern due to complexation with the salt. In many applications the uncoated surface of the donor (CB) sheet comprises a form of some type. The stylus pressure is generated by means of a pen or other writing instrument used in filling out the form. Thus, the image appearing on the receptor (CF) sheet is a copy of the image applied to the top sheet.
In some applications, multiple form sets have been used. These contain intermediate sheets having a metal salt coating on one side and a coating with capsules of ligand on the opposite side. Such sheets are generally referred to herein as "CFB" sheets (i.e., coated front and back sheets).
Due to the stoichiometry of the system (i.e., the metal salt is usually in excess since relatively little ligand is released), it is generally believed that the image formed on the receptor sheet, after stylus pressure is applied to break the capsules and release the ligand, results from the formation of a complex between one molecule of color-forming ligand and 1 or 2 atoms of a metal having a +2 valence (as for example Ni.sup.2+). The counterion of the positively charged transition metal is usually the conjugate base of a weak acid and may facilitate removal of the two protons from the color-forming ligands, necessary for complexation with the M.sup.2+ cation.
In commercial applications, generally, nickel salts have been preferred as the transition metal salts. One reason for this is that nickel salts form a deep color when complexed with the dithiooxamide ligands. The nickel salts are also substantially colorless, and thus do not alone impart color to the receptor (CF) sheet. A third reason is that nickel salts are relatively low in cost, by comparison to other transition metal salts that can be easily and safely handled and that form highly colored coordination complexes with dithiooxamides.
In some applications it is also desirable that the color of the complex be a deep, strong color that is not only pleasing to the eye, but that will exhibit good contrast with the paper, for purposes of later reading and/or photocopying. This has been one drawback with conventional carbonless paper arrangements, which use nickel salts complexed with disubstituted dithiooxamide ligands. The image imparted by the resulting coordination compound, under such circumstances, is generally magenta. The more "red" character the polymer complex exhibits, generally, the less contrasting and pleasing is the appearance. A dark, i.e., preferably black, blue, or blue-black, arrangement would be preferred, but previously such has not been satisfactorily obtainable. Recently, an attempt to achieve a blue or blue-black image by employing encapsulated N-(monosubstituted)dithiooxamides compatible with the transition metal chemistry described above was described (see U.S. Pat. No. 5,124,308). Preparation of these N-(monosubstituted)dithiooxamides is described in U.S. Pat. No. 5,041,654 which is incorporated herein by reference for the disclosure and synthesis of these N-(monosubstituted) dithiooxamides. These may be used either alone or in admixture with N,N'-(disubstituted)dithiooxamides and can result in a cyan, blue, or blue-black image. A neutral black image would be preferred but has still not been satisfactorily obtainable.
One attempt to prepare a neutral black image using metal coordination chemistry of this type was provided by Yarian. See D. R. Yarian, U.S. Pat. No. 4,334,015 (1982). He found that the combination of certain aromatic-substituted hydrazones with dithiooxamides followed by encapsulation of the mixture provides a method of achieving a dark image. These hydrazones react with the metal on the receiving sheet to form intense yellow images. The yellow coordination compound thus formed, combined with the blue-purple image formed by the dithiooxamide (such as N,N'-di(2-octanoyloxyethyl)dithiooxamide and/or N,N'-dibenzyldithiooxamide), results in an image that appears almost black to the observer.
Although this is a successful approach, Yarian's use of hydrazones still suffers from several drawbacks. The solubility of the hydrazones is not as great in the solvents generally used in the encapsulation process as are dithiooxamides. In addition, the initial image color of the coordination compound formed with N,N'-(disubstituted)dithiooxamide is brown and only after some time does the blue-black to black final image color form. Although much better than the blue-purple coordination compound formed with the N,N'-(disubstituted)dithiooxamide, this mixture of yellow and blue-purple is a dark blue-black rather than the preferred neutral black.
Yarian also noted that the color of capsules prepared from hydrazone compounds was pH dependent and their color may change from essentially colorless at low pH to yellow at pH greater than 9.5 to 10. Yarian further noted that this color change is rapid and reversible upon lowering of the pH. Papers can be divided into classes depending upon their methods of manufacture, treatment and sizing. Among these classifications are acidic and alkaline papers. Encapsulated hydrazones when coated onto "alkaline paper" can form yellow colors.
The ligands generally useful in carbonless paper constructions should also be relatively nonvolatile, so that free ligand, which would result from any inadvertently ruptured capsule, does not readily transfer from the donor sheet to the receptor sheet and form undesired spots of imaged area. That is, so that without the specific assistance of stylus or key pressure, transfer is not readily obtained.
In conventional impact imaging constructions, the capsules can be inadvertently ruptured in steps such as processing, printing, cutting, packaging, handling, storing, and copying. In these situations inadvertent marking or discoloration (i.e., backgrounding) of the sheets results due to inadvertent capsule rupture and transfer of the encapsulated material to the mating sheet where color formation occurs. The amount of inadvertent backgrounding has been reduced in such products by the use of a color control coreactant distributed externally among the capsules. This coreactant is capable of reacting with the contents of the ruptured capsules before transfer of said contents to the receptor sheet and formation of an undesired image. See D. A. Ostlie, U.S. Pat. No. 3,481,759 (1969). Ostlie discovered that addition of a small amount of a metal salt such as a zinc salt to the capsule coating prevents the formation of colored background. The zinc metal ion reacts with the accidently released dithiooxamide compound to form colorless coordination compounds and thus deactivates adventitiously released dithiooxamide materials.
The use of Yarian's invention in combination with that of Ostlie is not possible as zinc forms yellow coordination complexes with the hydrazones of Yarian's invention. Thus, yellow color backgrounding still occurs on the backside of the sheet due to inadvertently ruptured capsules. It would be desireable to have a yellow color-former that could be successfully deactivated by the same method as that described by Ostlie's discovery. Then, the same method of deactivation of the yellow, magenta, and cyan color-formers released by inadvertent capsule rupture would be possible.
Another approach to formation of a black image employs an encapsulated mixture of an acid sensitive green-forming leuco dye and a dithiooxamide color-former. The receptor sheet is formulated to contain phenolic type acids in addition to the transition metal salts. In this system, pressure imaging results in the release of both acid sensitive leuco dyes and dithiooxamide materials. The nickel salt in the receptor sheet reacts with the dithiooxamide to form a purple color and the phenolic acid in the receptor sheet reacts with the acid-sensitive leuco to form a green color. Together they generate a black image. This approach, while successful, has several disadvantages. Heavy coatings to the papers are required as two separate chemistries are involved. Another drawback of this approach is that the rates of reaction for the two chemistries are different and must be balanced by adjustment of the ratios of the two chemistries in the paper construction.
It is also preferred that the ligands should be colorless, since the ligands are often encapsulated and coated onto the backside of a sheet, such as a form, which has printing on one or both sides thereof. This allows for good legibility of printing on the back side of the carbonless copy-paper sheets. This aspect is particularly important if the donor sheet comprises a top sheet for a stack of carbonless papers. Such sheets are often white, so that they can be readily identified as originals, can be readily photocopied, and can be easily read. The presence of color in the coating on the back side of this sheet would detract from the white colored "original" appearance and could make photocopying of this sheet troublesome.
While the above-described preferred characteristics have long been desirable, they have not been satisfactorily achieved with conventional reactants and conventional constructions. What has been needed has been suitable materials and arrangements for achieving the desired features described.